This invention relates to a semiconductor device having a support member such as a lead frame to which a semiconductor die or chip is attached using a die-bonding material and encapsulated with resin, and a process for the fabrication of such a semiconductor device.
As methods by which semiconductor chips are attached to lead frames, a method has been used in which a die-bonding material is fed onto the lead frame and the semiconductor chip is bonded thereto.
Such a die-bonding material is known to include, e.g., Auxe2x80x94Si eutectics, solders and resin pastes. Of these, Auxe2x80x94Si eutectics have problems in that they are expensive, have a high modulus of elasticity, and require vibration at the bonding portion. The solders have problems in that they can not withstand temperatures equal to or greater than their melting temperature and have a high modulus of elasticity.
As for the resin pastes, silver paste is the most commonly available. Compared with other materials, silver paste is inexpensive, has a high heat resistance reliability and has a low modulus of elasticity. Hence, they are most widely used as bonding materials for the lead frames of ICs and LSIs.
In recent years, there has been a rapid increase in demand for high-density packaging as electronic machinery has been made smaller in size and thickness. In semiconductor packaging, conventional pin insertion packaging has been substituted by surface packaging, which has become the prevailing packaging method suitable for high-density packaging.
In surface packaging, in order to directly solder leads to printed-wiring substrates, packaging is carried out by infrared reflowing, vapor phase reflowing or solder dipping while heating the whole package.
During this packaging, the whole package is exposed to high temperatures of 210xc2x0 C. to 260xc2x0 C. Hence, any presence of moisture in the package cause explosive vaporization of the moisture to cause package cracks (hereinafter xe2x80x9creflow cracksxe2x80x9d).
Such reflow cracks may cause a great lowering of the reliability of semiconductor packages, bringing about a serious technical problem.
The mechanism by which reflow cracks ascribable to die-bonding materials occur is as follows: During storage of semiconductor packages, (1) die-bonding materials absorb moisture, (2) this moisture is vaporized upon heating when packaged by reflowing and soldering, and (3) vapor pressure thus produced causes breaking or separation of the die-bonding material layers, (4) so that the reflow cracks occur.
While reflow crack resistance of encapsulant has been improved, the reflow cracks ascribable to die-bonding materials provide a serious matter especially in thin-type packaging. Thus, it is strongly sought to improve its reflow crack resistance.
The silver paste, having been most commonly used, tends to cause reflow cracks because it has become difficult with the increase in size of chips to uniformly coat the silver paste on the whole surface requiring area and also because it is pasty itself and therefore tends to cause voids in bonding layers.
The present invention provides a semiconductor device that employs a filmy organic die-bonding material, may cause no reflow cracks and has good reliability, and a process for fabrication thereof.
In the present invention, a filmy organic die-bonding material is used. This filmy organic material is such a filmy material that is mainly made of an organic material such as epoxy resin, silicone resin, acrylic resin, or polyimide resin (including and organic material containing a metal filler or an inorganic material filler added thereto). The filmy organic die-bonding material which has been heated is contact-bonded to a support member such as a lead frame, and a semiconductor chip is placed on the filmy organic die-bonding material and heat is applied to bond the chip. More particularly, resin paste is provided in the form of a film so that die-bonding material is uniformly applied to the bonding portion.
FIG. 1 illustrates an example of a process for fabricating the semiconductor device of the present invention.
The filmy organic die-bonding material 1 is contact-bonded to a die pad 6 of a lead frame 5 on a heating platen 7 by means of a contact press ((b) in FIG. 1). The contact bonding may preferably be carried out under conditions of a temperature of from 200xc2x0 C. to 250xc2x0 C., a press time of from 0.1 second to 20 seconds and a pressure of from 4 gf/mm2 to 200 gf/mm2.
A semiconductor chip 8 is put on the filmy organic die-bonding material 1 stuck to the die pad 6, followed by heat contact bonding (i.e., die bonding) ((c) in FIG. 1). The die bonding may preferably be carried out under conditions of a temperature of from 100xc2x0 C. to 350xc2x0 C., a bonding time of from 0.1 second to 20 seconds and a pressure of from 0.1 gf/mm2 to 30 gf/mm2. More preferably conditions for die bonding are of a temperature of from 150xc2x0 C. to 250xc2x0 C., a bonding time of 0.1 (inclusive) second to 2 seconds and a pressure of 0.1 gf/mm2 to 4 gf/mm2, and the most preferable conditions for die bonding are of a temperature of from 150xc2x0 C. to 250xc2x0 C., a bonding rime of 0.1 (inclusive) second to 1.5 (exclusive) seconds and a pressure of 0.3 gf/mm2 to 2 gf/mm2.
Then, the step of wire bonding ((d) in FIG. 1 follows, and the step of encapsulating the semiconductor chip with resin ((e) in FIG. 1) further follows. Thus, the semiconductor device is produced. Reference numeral 9 denotes and encapsulant resin.
For example, the filmy organic die-bonding material of the present invention is prepared by dissolving or dispersing an organic material such as polyimide or epoxy resin and optionally and additive such as a metal filler in an organic solvent to obtains a coating varnish, coating this coating varnish on a carrier film such as biaxially stretched polypropylene film, followed by evaporation of the solvent, and peeling the filmy material from the carrier film. When prepared in this way, a film having self-supporting properties can be obtained.
The present inventors have discovered that the occurrence of reflow cracks in semiconductor device correlates with the properties or characteristics of the filmy organic die-bonding material, and have made detailed studies on the relationship between the occurrence of reflow cracks and the characteristics of the filmy organic die-bonding material. As a result, they have accomplished the present invention.
According to a first embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and encapsulated with resin, a filmy organic die-bonding material having a water absorption of 1.5% by volume or less is used as the die-bonding material.
According to a second embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material having a saturation moisture absorption of 1.0% by volume or less is used as the die-bonding material.
According to a third embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material having a residual volatile component in an amount not more than 3.0% by weight is used as the die-bonding material.
According to a fourth embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material having a modulus of elasticity of 10 Mpa or less at a temperature of 250xc2x0 C. is used as the die-bonding material.
According to a fifth embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material having, at the stage where the semiconductor chip is bonded to the support member, a void volume of 10% or less in terms of voids present in the die-bonding material and at the interface between the die-bonding material and the support member is used as the die-bonding material.
According to a sixth embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material having a peel strength of 0.5 Kgf/5xc3x975 mm chip or above at the stage where the semiconductor chip is bonded to the support member is used as the die-bonding material.
According to a seventh embodiment of the present invention, the semiconductor device and the process for its fabrication are characterized in that, in the semiconductor device having a support member to which a semiconductor chip is attached using a die-bonding material and then encapsulated with resin, a filmy organic die-bonding material i) having a planar dimension not larger than the planar dimension of the semiconductor chip, and ii) not protruding outward from the region of the semiconductor chip (i.e., not to protrude from the interface between the semiconductor chip and the support member) at the stage where the semiconductor chip is bonded to the support member is used as the die-bonding material.
In the embodiments of the present invention, the values of the properties or characteristics of the filmy organic die-bonding materials, such as a water absorption of 1.5% by volume or less, a saturation moisture absorption of 1.0% by volume or less, a residual volatile component in an amount not more than 3.0% by weight, or a modulus of elasticity of 10 MPa or less at a temperature of 250xc2x0 C., are the values measured at the stage before the filmy organic die-bonding material is stuck onto the support member.
The filmy organic die-bonding material used in the first embodiment of the present invention, having a water absorption of 1.5% by volume or less, the filmy organic die-bonding material used in the second embodiment of the present invention, having a saturation moisture absorption of 1.0% by volume or less, the filmy organic die-bonding material used in the fourth embodiment of the present invention, having a modulus of elasticity of 10 MPa or less at a temperature of 250xc2x0 C., and the filmy organic die-bonding material used in the sixth embodiment of the present invention, having a peel strength of 0.5 Kgf/5xc3x975 mm chip or above at the stage where the semiconductor chip is bonded to the support member, can be produced by controlling composition of the filmy organic die-bonding material, e.g., the structure of polymers such as polyimide and the content of fillers such as silver.
The filmy organic die-bonding material used in the third embodiment of the present invention, having a residual volatile component in an amount not more than 3.0% by weight, and the filmy organic die-bonding material used in the fifth embodiment of the present invention, having, at the stage where the semiconductor chip is bonded to the die-bonding material, a void volume of 10% or less in terms of voids present in the die-bonding material and at the interface between the die-bonding material and the support member, can be produced by controlling the conditions for producing the filmy organic die-bonding material, e.g., drying temperature, drying time and so forth.
The semiconductor chip includes commonly available semiconductor chips of ICs, LSIs, VLSIs and so forth, any of which may be used. The die bonding materials according to the present invention is suitably used for the semiconductor chip as large a 5xc3x975 mm or larger. The support member includes lead frames having die pads, ceramic wiring boards and glass-polyimide wiring boards, any of which may be used. FIG. 3 shows a plan view of an example of lead frames having die pads. The lead frame 40 shown in FIG. 3 has die pads 41.
As the filmy organic die-bonding material, not only those having single-layer structure but also those having multi-layer structure may be used.
In the present invention, the filmy organic die-bonding material may have at the same time two or more properties or characteristics of those described above.
For example, properties or characteristics the filmy organic die-bonding material may preferably have at the same time are as follows;
(1) A filmy organic die-bonding material having a saturation moisture absorption of 1.0% by volume or less and a residual volatile component in an amount not more than 3.0% by weight;
(2) A filmy organic die-bonding materiel having a saturation moisture absorption of 1.0% by volume or less, and a peel strength of 0.5 Kgf/5xc3x975 mm chip or above at the stage where the semiconductor chip is bonded to the support member;
(3) A filmy organic die-bonding material having a residual volatile component in an amount not more than 3.0% by weight and a peel strength of 0.5 Kgf/5xc3x975 mm chip or above at the stage where the semiconductor chip is bonded to the support member, and
(4) A filmy organic die-bonding material having a saturation moisture absorption of 1.0% by volume or less, a residual volatile component in an amount not more than 3.0% by weight, and a peel strength of 0.5 Kgf/5xc3x975 mm chip or above at the stage where the semiconductor chip is bonded to the support member.
In the present invention, the foregoing properties or characteristics of the filmy organic die-bonding material may be in any combination in accordance with the purposes for which it is used.
The above (1) to (4) filmy organic die-bonding materials or the filmy organic die-bonding materials having the above properties or characteristics in any other combinations may preferably be used as filmy organic die bonding materials each i) having a planar dimension not larger than the planar dimension of the semiconductor chip, and ii) not protruding outward from the region of the semiconductor chip at the stage where the semiconductor chip is bonded to the support member.
The semiconductor device of the present invention is free from reflow cracks which might otherwise occur during reflow soldering for the packaging of semiconductor devices, and has good reliability.
As the organic material constituting the filmy organic die-bonding material of the present invention, polyimide resin is preferred,
Tetracarboxylic dianhydrides used as starting materials for the polyimide resin include:
1,2-(ethylene)bis(trimellitate anhydride),
1,3-(trimethylene)bis(trimellitate anhydride),
1,4-(tetramethylene)bis(trimellitate anhydride),
1,5-(pentamethylene)bis(trimellitate anhydride),
1,6-(hexamethylene)bis(trimellitate anhydride),
1,7-(heptamethylene)bis(trimellitate anhydride),
1,8-(octamethylene)bis(trimellitate anhydride),
1,9-(nonamethylene)bis(trimellitate anhydride),
1,10-(decamethylene)bis(trimellitate anhydride),
1,12-(dodecamethylene)bis(trimellitate anhydride),
1,16-(hexadecamethylene)bis(trimellitate anhydride),
1,18-(octadecamethylene)bis(trimellitate anhydride), pyromellitic dianhydride,
3,3xe2x80x2,4,4xe2x80x2-diphenyltetracarboxylic dianhydride,
2,2xe2x80x2,3,3xe2x80x2-diphenyltetracarboxylic dianhydride,
2,2-bis(3,4-dicarboxyphenyl)propone dianhydride,
2,2-bis(2,3-dicarboxyphenyl)propane dianhydride,
1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride,
1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride,
bis(2,3-dicarboxyphenyl)methane dianhydride,
bis(3,4-dicarboxyphenyl)methane dianhydride,
bis(3,4-dicarboxyphenyl)sulfone dianhydride,
3,4,9,10-perylenetetracarboxylic dianhydride,
bis(3,4-dicarboxyphenyl)ether dianhydride,
benzene-1,2,3,4-tetracarboxylic dianhydride,
3,4,3xe2x80x2,4xe2x80x2-benzophenonetetracarboxylic dianhydride,
2,3,2xe2x80x2,3xe2x80x2-benzophenonetetracarboxylic dianhydride,
2,3,3xe2x80x2,4xe2x80x2-benzophenonetetracarboxylic dianhydride,
1,2,5,6-naphthalenetetracarboxylic dianhydride,
2,3,6,7-naphthalenetetracarboxylic dianhydride,
1,2,4,5-naphthalene-tetracarboxylic dianhydride,
1,4,5,6-naphthalene-tetracarboxylic dianhydride,
2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,
2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,
2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,
phenanthrene-1,8,9,10-tetracarboxylic dianhydride,
pyrazine-2,3,5,6-tetracarboxylic dianhydride,
thiophene-2,3,4,5-tetracarboxylic dianhydride,
2,3,3xe2x80x2,4xe2x80x2-biphenyltetracarboxylic dianhydride,
3,4,3xe2x80x2,4xe2x80x2-biphenyltetracarboxylic dianhydride,
2,3,2xe2x80x2,3xe2x80x2-biphenyltetracarboxylic dianhydride,
bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride,
bis(3,4-dicarboxyphenyl)methylphenylsilane dianhydride,
bis(3,4-dicarboxyphenyl)diphenylsilane dianhydride,
1,4-bis(3,4-dicarboxyphenyldimethylsilyl)benzene dianhydride,
1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldicyclohexane dianhydride
p-phenylenebis(trimellitate anhydride),
ethylenetetracarboxylic dianhydride,
1,2,3,4-butanetetracarboxylic dianhydride,
decahydronaphthalene-1,4,5,8-tetracarboxylic dianhydride,
4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride,
cyclopentane-1,2,3,4-tetracarboxylic dianhydride,
pyrrolidine-2,3,4,5-tetracarboxylic dianhydride,
1,2,3,4-cyclobutanetetracarboxylic dianhydride,
bis(exo-bicyclo[2,2,1]heptane-2,3-dicarboxylic dianhydride)sulfone,
bicyclo-(2,2,2)-octo-7-ene-2,3,5,6-tetracarboxylic dianhydride,
2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride,
2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)hexafluoropropane dianhydride,
4,4xe2x80x2-bis(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride,
1,4-bis(2-hydroxyhexafluoroisopropyl)benzenebis(trimellitic anhydride),
1,3-bis(2-hydroxyhexafluoroisopropyl)benzenebis(trimellitic anhydride),
5-(2,5-dioxotetrahydrofuril)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, and
tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride.
Any of these may be used in the form of a mixture of two or more kinds.
Diamines used as starting materials for the polyimide resin include aromatic diamines such as:
o-phenylenediamine,
m-phenylenediamine,
p-phenylenediamine,
3,3xe2x80x2-diaminodiphenyl ether,
3,4xe2x80x2-diaminodiphenyl ether,
4,4xe2x80x2-diaminodiphenyl ether,
3,3xe2x80x2-diaminodiphenylmethane,
3,4xe2x80x2-diaminodiphenylmethane,
4,4xe2x80x2-diaminodiphenylmethane,
bis(4-amino-3,5-dimethylphenyl)methane,
bis(4-amino-3,5-diisopropylphenyl)methane,
3,3xe2x80x2-diaminodiphenyldifluoromethane,
3,4xe2x80x2-diaminodiphenyldifluoromethane,
4,4xe2x80x2-diaminodiphenyldifluoromethane,
3,3xe2x80x2-diaminodiphenyl sulfone,
3,4xe2x80x2-diaminodiphenyl sulfone,
4,4xe2x80x2-diaminodiphenyl sulfone,
3,3xe2x80x2-diaminodiphenyl sulfide,
3,4xe2x80x2-diaminodiphenyl sulfide,
4,4xe2x80x2-diaminodiphenyl sulfide,
3,3xe2x80x2-diaminodiphenyl ketone,
3,4xe2x80x2-diaminodiphenyl ketone,
4,4xe2x80x2-diaminodiphenyl ketone,
2,2-bis(3-aminophenyl)propane,
2,2xe2x80x2-(3,4xe2x80x2-diaminodiphenyl)propane,
2,2-bis(4-aminophenyl)propane,
2,2-bis(3-aminophenyl)hexafluoropropane,
2,2-(3,4xe2x80x2-diaminodiphenyl)hexafluoropropane,
1,2-bis(4-aminophenyl)hexafluoropropane,
1,3-bis(3-aminophenoxy)benzene,
1,4-bis(3-aminophenoxy)benzene,
1,4-bis(4-aminophenoxy)benzene,
3,3xe2x80x2-(1,4-phenylenebis(1-methylethylidene))bisaniline
3,4xe2x80x2-(1,4-phenylenebis(1-methylethylidene))bisaniline
4,4xe2x80x2-(1,4-phenylenebis(1-methylethylidene))bisaniline
2,2-bis(4-(3-aminophenoxy)phenyl)propane,
2,2-bis(4-(4-aminophenoxy)phenyl)propane,
2,2-bis(4-(3-aminophenoxy)phenyl)hexafluoropropane,
2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane,
bis(4-(3-aminophenoxy)phenyl)sulfide,
bis(4-(4-aminophenoxy)phenyl)sulfide,
bis(4-(3-aminophenoxy)phenyl)sulfone, and
bis(4-(4-aminophenoxy)phenyl)sulfone;
and aliphatic diamines such as:
1,2-diaminoethane,
1,3-diaminopropane,
1,4-diaminobutane,
1,5-diaminopentane,
1,6-diaminohexane,
1,7-diaminoheptane,
1,8-diaminooctane,
1,9-diaminononane,
1,10-diaminodecane,
1,11-diaminoundecane, and
1,12-diaminododecane.
Any of these may be used in the form of a mixture of two or more kinds.
The polyimide can be obtained by subjecting the tetracarboxylic dianhydride and the diamine to condensation by a known method. More specifically, using the tetracarboxylic dianhydride and the diamine in substantially equimolar weights (the respective components may be added in any order), the reaction is carried out in an organic solvent at a reaction temperature of 80xc2x0 C. or below, and preferably at 0xc2x0 C. to 50xc2x0 C. With the progress of the reaction, the viscosity of reaction mixture gradually increases, so that a polyimide precursor polyamic acid is formed.
The polyimide can be obtained by dehydration ring closure of the above reaction product (polyamic acid). The dehydration ring closure may be carried out by a method of heat treatment at 120xc2x0 C. to 250xc2x0 C. or by a chemical method.
Epoxy resin of glycidyl ether type, glycidylamine type, glycidyl ester type or alicyclic type may be used as organic materials for the filmy organic die-bonding materials of the present invention.
As mentioned above, in the process for the fabrication of a semiconductor device according to the present invention, the die bonding may preferably be carded out under conditions of a temperature of from 100xc2x0 C. to 350xc2x0 C., a bonding time of from 0.1 second to 20 seconds and a pressure of from 0.1 gf/mm2 to 30 gf/mm2. More preferably, it is carried out under conditions of a temperature of from 150xc2x0 C. to 250xc2x0 C., a bonding time of 0.1 (inclusive) second to 2 seconds and a pressure of 0.1 gf/mm2 to 40 gf/mm2, and the most preferably, under conditions of from 150xc2x0 C. to 250xc2x0 C., a bonding time of 0.1 (inclusive) second to 1.5 (exclusive) seconds and a pressure of 0.3 gf/mm2 to 2 gf/mm2.
When a filmy organic die-bonding material whose elastic modulus at a temperature of 250xc2x0 C. Is not more than 10 MPa is used, a sufficient peel strength (for example, 0.5 Kgf/5xc3x975 mm chip or more) can be obtained by carrying out die-bonding under conditions of a temperature of from 150xc2x0 C. to 250xc2x0 C., a bonding time of 0.1 (inclusive) second to 2 seconds and a pressure of 0.1 gf/mm2 to 4 gf/mm2.